Dosage Forms
Delivery of medication to a patient is often in the form of a tablet, liquid formulation or powder for reconstitution. Each dosage form has disadvantages. Patients are often unwilling, or unable, to swallow tablets, especially when the tablets are relatively large, or when an effective dose requires ingestion of multiple tablets. Challenges associated with swallowing tablets are particularly relevant for children and older adults. Likewise, some patients are unwilling, or unable, to drink liquid pharmaceutical formulations due to an undesirable taste and/or mouth feel.
When the amount of a specific active ingredient to be administered exceeds the amount that can be conveniently formulated in a tablet, the dosage is often provided as a powder or liquid concentrate. The powder or concentrate is then reconstituted for administration as an oral liquid, syrup or powder suspension. The preparation of a liquid formulation from a powder or liquid concentrate can be inconvenient or cumbersome, especially when the patient must take the medication chronically or frequently. This may result in reduced patient compliance and ultimately, in reduced effectiveness of the treatment regimen.
A single dosage form that can be administered as either an immediate release tablet or liquid provides options for patients, caregivers and hospitals when administering a medication to patients who prefer, or are unable, to take one form of medication or the other. For instance, a dual purpose tablet that can be swallowed whole or disintegrated in liquid prior to ingestion would be useful for patients able to swallow tablets, or for patients who prefer or require a medication in a liquid form, or for patients to whom the liquid is directly administered (e.g. delivery through a feeding tube).
Sodium Sulfate
Sodium sulfate is an abundant, naturally occurring salt known to have a laxative effect. However, formulating sodium sulfate in dosage forms, either for direct oral ingestion or in aqueous solution is quite challenging, stemming, at least in part, from the levels of salt required to achieve the desired laxative effect and, further, from the extreme hygroscopic nature and unique solubility profile of sodium sulfate.
With respect to formulating sulfate salts in tablet form for direct oral ingestion, the challenge stems, at least in part, from formulating a convenient dosage form containing a high level and/or effective amount of sodium sulfate to achieve the desired laxative effect. The laxative effect of sulfate salts requires approximately between 2 to 7 grams of sulfate ion and/or 3 to 11 grams of sulfate salts. However, until now, formulating tablets with a high level of sodium sulfate at a size appropriate for direct ingestion while minimizing the number of tablets required to induce laxation has proved challenging.
In addition, the extreme hygroscopic properties of sodium sulfate make the provision of a tablet formulation difficult. When placed in the mouth, the sodium sulfate immediately scavenges all available saliva creating an undesirable mouth feel and dry mouth, thereby making swallowing difficult.
With respect to formulating a tablet dosage form of sodium salt for disintegration in water, the chemical properties of sodium sulfate present significant challenges. Sodium sulfate exhibits unusual water solubility characteristics in that its solubility increases more than 10-fold from 0° C. to 32.384° C. At 32.384° C. the solubility curve changes and crystal water is released and the hydrated salt melts. In contrast to other salts (e.g., potassium, magnesium), the solubility of sodium sulfate does not increase with increasing temperature above 32.384° C. Due to these solubility characteristics, sodium sulfate will crystallize when concentrated and/or cooled.
The reaction of sodium sulfate and water is exothermic, generating heat during hydration and causing the localized water temperature to increase significantly. When sodium sulfate is added to ambient temperature water with no agitation, the water wets the sodium sulfate which is converted to sodium decahydrate and creates an exothermic reaction in the immediate physical area. The exothermic reaction can increase the temperature of the localized wetted salt by as much as 10° C. This results in a portion of the sodium sulfate dissolving to form a localized concentrated solution. However, as the heat from the reaction dissipates into the surrounding solution, the temperature of the localized high concentration sodium sulfate solution decreases and the sodium sulfate recrystallizes forming a very hard mass of sodium sulfate decahydrate (i.e., mirabilite).
Until now, acceptable tablets capable of rapidly disintegrating in water could only be achieved with the inclusion of a high level of inactive ingredients and excipients, which significantly increases the weight and mass of the final dosage formulation and potentially doubles the number of tablets needed to deliver an effective dose. Indeed, formulating tablets of sulfate salts for dispersion in water required about 50% to 90% of excipient, thereby limiting the levels of sulfate salts present therein.
For these reasons, formulation scientists have sought to formulate sulfate salts at the dosage levels necessary to achieve laxation in a powdered form for reconstitution or as a liquid or syrup.
Other forms of tablets include buccal tablets, sublingual tablets, chewable tablets and effervescent tablets. However, these formulations fail to address (i) the need for a versatile and convenient formulation to address patient compliance issues, and (ii) the need for a formulation of a high dose of sodium sulfate to achieve the desired laxative effect.
Dual use tablets of tetracycline have been proposed (see, U.S. Pat. No. 5,211,958; “Pharmaceutical Composition and Process for its Preparation”). However, the unique properties of sodium sulfate as described above do not allow for mere application of the teachings of proposed dual use tablets of alternative active agents to formulating dual use sodium sulfate tablets having a high level of active agent. In addition, the proposed tetracycline tablets include greater than 50% by weight of excipient. Moreover, the tetracycline tablets previously proposed have not been shown to be capable of disintegration in cool or cold water. Typical drinking water sources provide water at temperatures less than 20° C. An acceptable dual use tablet composition should perform as claimed throughout all typical drinking water temperatures.